How can I and what do I use to create digital art like these examples?

They appear to be created in both Corel Painter and Adobe Photoshop. It's best to take a class, but if you are a self motivated individual, you can learn on your won with tutorials and books, Try your bookstore for books on Photoshop Compositing and Masking, you will need to know this to take your photos and blend them. Plus you can find books on digital art for Photoshop. A good place to start on knowing the basics is by getting video tutorials. Try Lynda.com (They cover every software) or try doing a search on You Tube for Photoshop and Painter Tutorials. Best of Luck and Have Fun!

The first and third look like photoshop. The second looks like painter. It might be good to take a summer class.

Attain a program such as Photoshop. Check in to getting a wacom tablet. Read lots of tutorials on deviantart and across the web. Experiment, experiment, experiment. Those are all digital paintings. Some start as a hand drawn sketch that is scanned in and painted and some are free hand in the program itself. The best thing is to try it out!